The cardiovascular system is a complex web of tens of thousands of miles of arteries, capillaries, and veins. Researchers at Lawrence Livermore National Laboratory are duplicating this intricate network using an emerging technology - 3D bioprinting. Using a 3D printer and a “bio-ink” made of materials compatible with the human body, the research team has successfully printed structures with living cells and biomaterials. The material and environment are engineered to enable small blood vessels, human capillaries, to develop on their own. This process takes a while, so initially, tubes are printed out of cells and other biomaterials to deliver essential nutrients to the surrounding printed environment. Eventually, the self-assembled capillaries are able to connect with the bio-printed tubes and deliver nutrients to the cells on their own, enabling these structures to function like they do in the body.